Such cards may be of the “contactless” type, since they only include a “contactless” interface or of the “dual interface” type since they include two interfaces: a first “contactless” interface and a second interface using external electric contacts for establishing a so-called “contact” communications.
In both of these types of chip cards, the body of the card generally includes an antenna circuit comprising the near field communications antenna and a microcircuit electrically connected to both ends of the antenna. The microcircuit thus forms a communications module, also designated by NFC (Near Field Communication) module.
A user of such a card may access various wireless services, such as for example secured electronic payment services, door-opening services or may exchange information with a device for contactless reading of the card adapted to NFC technology.
In order to use this type of services or for exchanging information, the user brings his/her mobile terminal closer to such a reading device, such as for example a payment terminal or an access terminal, so that near field communications may be established.
It is known from the state of the art how to equip such cards with an indicator light capable of being lit when near field communication is established. This notably allows the user of the card to be informed on proper progress of the communication or, on the contrary, on its failure.
The indicator light for example comprises a light-emitting diode capable of emitting light when a current of predefined intensity flows through it. The diode is then connected to the antenna circuit in such a way that, when the card is placed in proximity to the card reader, a current flows in the antenna circuit causing light emission from the diode.
The diode usually comprises a semiconducting junction capable of emitting light with a predefined color when it is activated and a lid, i.e. a transparent external casing for protecting this junction.
The predefined emission color of the diode notably depends on its semiconducting junction. It is thereby possible to obtain different colors of indicator lights by changing the nature of the semiconducting junction of the diode.
For aesthetic reasons, it may then be of interest to select the color of the diode depending on a display of the card. For example, selecting a diode of yellow color for representing a sun, a diode of red color for representing an alarm indicator light, etc.
Now, the configuration of the antenna circuit and of the diode should be selected so as to define together a resonance frequency substantially corresponding to a predefined near field communication frequency such as for example the one defined by the ISO 14443 standard, substantially equal to 13.56 MHz.
This resonance frequency notably depends on the sizes and on the shape of the antenna as well as on the capacitance of the semiconducting junction of the diode.
As a result, in order to produce two distinct cards with indicator lights with distinct colors, two diodes have to be available, having distinct semiconducting junctions and therefore distinct electric capacitances.
Thus, in order to obtain a resonance frequency substantially equal to the predefined near field communication frequency, the shape and the dimensions of the antenna circuit are adjusted by taking into account the electric characteristics of the diode, and notably those of the semiconducting junction.
The drawback is that this causes additional production costs and developments. Indeed, for each card display requiring a new color of indicator light, the antenna circuit has to be considerably modified and many adjustments or changes in the production equipment have to be carried out, which may prove to be relatively long and costly.